Metallic glass alloys are amorphous alloys. Because amorphous alloys do not have long range ordered structures, they do not share some of the problems associated with ordinary metals having a single crystalline structure, or having a poly-crystalline structure with grains and grain boundaries. As a result, metallic glass alloys have been made with various desirable properties, such as strength, elasticity, corrosion resistance, and low surface friction, to name just a few examples.
Historically, rapid cooling was required to bring about the amorphous structure as an alloy was cooled. As a result, because heat was needed to be extracted quickly, only relatively small-dimensioned products, such as ribbons or sheets, for example, were produced. Over the years, alloys were discovered that do not require such rapid cooling rates, so that casting methods may be employed to manufacture metallic glass alloys having larger-sized dimensions, such as having structures with thick layers over 1 mm. Such alloys are sometimes referred to as bulk-solidifying, or bulk, amorphous metallic alloys, and have found applications in diverse products and industries, such as the aerospace industry, sporting goods, consumer electronics, and medical devices and instruments. In medical applications, particularly in medical implants, low toxicity is of course desirable.
The bulk-solidifying amorphous alloys system of Pd—Cu—Ni—P is currently regarded as among the best bulk-glass forming metallic systems in terms of having the slowest cooling rate required to form a glass, or alternatively, in terms of the largest bulk object that may be solidified having an amorphous structure. The presence of Ni, however, hinders utilization of this alloy for biomedical implant applications, as Ni is considered toxic for biomedical use.
There has been recent work in substituting bio-compatible elements for Ni in the Pd—Cu—Ni—P alloys without significantly degrading its glass-forming ability. Two recent efforts toward this end involve substituting Pt or Si for Ni. Pt may be regarded as an effective substitute for Ni in the Pd—Cu—Ni—P system because it contributes to maintaining the glass-forming ability. However, its high market price contributes to a large increase in the cost of the resulting amorphous alloy, thereby making it less affordable for applications requiring large volumes of material. Si, on the other hand, is an inexpensive element and may contribute to a decrease in the cost of the resulting amorphous alloy. However, substitution of Si for Ni has so far not led to very practical amorphous alloys in terms of glass-forming ability.